Calculator keyboard switch with disc spring contact and printed circuit board

ABSTRACT

A keyboard switch assembly including a printed circuit board having four switch terminals on one side of the board, three of the terminals being arranged in a triangle and the fourth disposed within the triangle. Conductors on the one side of the board are respectively joined to the interior terminal and at least one of the three terminals. A conductive, generally triangular, snap-acting dome switch member is provided having arcuate apices, projections being respectively formed from the apices and respectively engaging the three terminals thereby spacing the periphery of the switch element from the one surface of the printed circuit board and the conductors thereon, at least the conductor connected to the interior terminal extending under the dome. The switch element has a fourth projection formed from the interior of the dome adjacent the center thereof which is in registry with the interior terminal and engages that terminal when the dome is deflected thereby completing an electrical circuit between the three terminals and the interior terminal. A layer of insulating material covers the conductors exclusive of the terminals. A sheet of insulating material covers the insulating layer and has an opening therein which receives and locates the switch member. Another sheet of insulating material covers the first sheet and the switch member. A plate covers the second insulating sheet and has an opening therein which receives a push button in registry with the switch element, depression of the push button actuating the dome of the switch member to a non-overcenter, deflected position in which the interior projection on the dome engages the interior switch terminal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a keyboard switch assembly of thetype used in electronic calculator apparatus.

2. Description of the Prior Art

Keyboard switches have been provided employing a conductive snap-actingdome member as the switch element, such keyboard switches being shownfor example in U.S. Pat. Nos. .Iadd.486,212, .Iaddend. 3,643,041 and3,684,842, German Pat. .[.Nos. 486,212 and.]. .Iadd.No..Iaddend.1,806,241, and IBM Technical Disclosure Bulletin No. 12, Vol.7, May, 1965, p. 1168 entitled "Snap-Action Membrane Switch Keyboard."Another keyboard switch assembly of the same general type manufacturedby Texas Instruments Incorporated employs a printed circuit board havingconductors on one surface thereof, staples extending through the boardfrom the other surface to the one surface and being soldered to selectedconductors thereon, and snap-acting domes cooperating with the portionsof the staples on the other side of the board to perform the switchingfunction, that assembly being shown in U.S. Pat. No. 3,727,907. Yetanother type of keyboard switch manufactured by .[.Colorodo.]..Iadd.Colorado .Iaddend.Instruments Corp. incorporates a printed circuitboard having conductors on both surfaces thereof, the board havingplated openings extending therethrough connected to certain conductors,and snap-acting domes cooperating with the plated openings to performthe switching function.

SUMMARY OF THE INVENTION

The keyboard switch assemblies of the type described above known to thepresent applicants employ some combination of double sided printedcircuit boards, soldered connections, and/or a conductive ground platein addition to a printed circuit board, these features complicatingassembly thus adding appreciably to the cost. It is therefore desirableto provide a keyboard switch assembly of the general type describedabove which utilizes a single sided printed circuit board and which doesnot require soldered connections or an additional conductive groundplate.

The present invention, in its broader aspects, is embodied in a keyboardswitch assembly including a push button manually actuable from aninactive to a switch-actuating position, and a conductive switch memberincluding a resilient element actuated by the push button from a normalto a deflected position, and comprises an insulative board havingopposite surfaces with one of the surfaces having first and secondconductors thereon, the first conductor including a first switchterminal portion and the second conductor including a second switchterminal portion. The switch element faces the one surface of theprinted circuit board and the conductors and has a first contact areathereon spaced from the center area of the element, the first contactarea engaging the first terminal portion. The center area of the elementforms a second contact area in registry with the second terminal portionand engaging the same when the element is in its deflected positionthereby electrically connecting the first and second terminal portionsand their respective conductors.

It is accordingly an object of the invention to provide an improvedkeyboard switch assembly.

Another object of the invention is to provide an improved keyboardswitch assembly of the type employing a conductive snap-acting domemember as the switch element.

A further object of the invention is to provide an improved keyboardswitch assembly of the type employing a snap-acting dome member as theswitch element in which a single sided printed circuit board is utilizedand soldered connections and/or conductive ground plates are eliminated.

The abovementioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a simplified, two-by-two XYkeyboard switching matrix;

FIG. 2 is a top view showing an insulative board with XY conductors andswitch terminals thereon arranged in a pattern in accordance with theinvention to provide the keyboard switch matrix of FIG. 1;

FIG. 3 is a cross-sectional view taken generally along the line.[.2--2.]. .Iadd.3--3 .Iaddend.of FIG. 2 and showing the basic switchingelement employed in the invention;

FIG. 4 is top view, partly broken away, showing the preferred embodimentof the improved keyboard switch assembly of the invention;

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 4;

FIG. 6 is an enlarged fragmentary view showing a portion of the printedcircuit board employed in the preferred embodiment;

FIG. 7 is a cross-sectional view taken along the line 7--7 of FIG. 6;

FIG. 8 is a top view showing the snap-acting dome switch member employedin the preferred embodiment;

FIG. 9 is a fragmentary view showing the configuration of one of theopenings in the switch element retaining member;

FIG. 10 is a fragmentary, exploded perspective view further showing thepreferred embodiment of the invention;

FIG. 11 is a fragmentary cross-sectional view showing another embodimentof the invention;

FIG. 12 is a top view of the switch element employed in the embodimentof FIG. 11;

FIG. 13 is a top view of a modified form of the switch element shown inFIGS. 11 and 12; and

FIG. 14 is a top view of a modified form of the switch element shown inFIGS. 4-10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, a keyboard switch assembly for an electronic device, such asa calculator, can be considered to be an XY grid or matrix of conductorswith the X conductors insulated from the Y conductors, a particularfunction being identified by making electrical contact between aselected X conductor and a selected Y conductor. Referring to FIG. 1 ofthe drawing, a simplified, two-by-two switching matrix is showncomprising X₁ and X₂ conductors respectively insulated from Y₁ and Y₂conductors, the switching functions being performed by switches S₁ - S₄.It will be understood that the number of X or Y conductors in thekeyboard matrix can be any integer equal to or larger than one, and thatthe number of possible switching functions is equal to the product ofthe number of X conductors and the number of Y conductors. Momentarycontact push button switches are customarily employed to make thenecessary contact between the X and Y lines.

The Texas Instruments keyboard switch assembly referred to above employsa single sided printed circuit board with the requisite insulation atthe XY crossovers being provided by conducting U-shaped staplesextending through the board with their legs soldered to the conductorson one side and their bight portions engaging the other side of theboard. The Colorado Instruments keyboard switch assembly referred toemploys a two-sided printed circuit board with the X conductors on oneside thereof and the Y conductors on the other, plated through-holesbeing used to provide X contacts on the same side of the board as the Ycontacts. In both of those assemblies, the printed circuit board servesas an insulator between the X and Y conductors with staples or platedthrough-holes being used to bring the X and Y contact points to theswitching side of the board.

In the keyboard switch assembly of the present invention, the thicknessof the printed circuit board is not used as an insulator between the Xand Y conductors, there being no conductors extending through the boardto provide electrical contact from one side to the other. Referring nowto FIGS. 2 and 3, in accordance with the invention an insulative board 1is provided having X and Y conductors secured to the switching sidethereof, the conductors being arranged in a pattern and having terminalportions 2, 3 arranged to cooperate with the respective switchingelements S so as to make contact between selected X and Y conductorswithout touching other conductors.

Switching elements S are formed of conductive, resilient material, eachswitching element S having edge or peripheral contact areas 5 engagingone or more Y terminal portions 2 and having a normal position, as shownin solid lines in FIG. 3, with it center contact area 6 spaced from arespective X terminal portion 3, switching element 4 also being spacedfrom other X and/or Y conductors, as shown. Upon application of adownward force on switching element 4, as shown by arrow 7, such as thatapplied by manual actuation of a push button, switching element 4 isdeflected to a position as shown in dashed lines at 4a with its centercontact area 6 making contact with a respective X terminal portion 3thus electrically connecting the respective X and Y conductors. It willbe observed that in its deflected position, switching .[.switching.].element 4 does not contact the other conductors, such as conductors Y₁therebeneath. Upon release of the downward force 7, switching element 4resiliently returns to its normal position thus breaking the electricalconnection between the respective X and Y conductors.

In FIG. 2, the orientation of switching elements S with the respective Xand Y terminal portions is shown in dashed lines. For example, switchingelement S1 may be of the type shown in FIG. 13, switching element S2 maybe of the type shown in FIGS. 4-10, switching element S3 may be the typeshown in FIG. 14, and switching element S4 may be the type shown inFIGS. 11 and 12, it being understood that all switching elements in agiven keyboard switch assembly will generally have the sameconfiguration.

Referring now to FIGS. 4 through 10 of the drawings, the preferredembodiment of the improved keyboard switch assembly of the invention,generally indicated at 10, comprises single sided printed circuit board12, snap-acting dome switch members 14, insulative switch memberretaining sheet 16, insulative cover sheet 18, cover member 20, and pushbuttons 22. Switch members 14 and insulative sheets 16, 18 aresandwiched between printed circuit board 12 and cover member 20 and thekeyboard switch assembly is held in assembled relation by rivets 24. Theillustrated embodiment of keyboard switch assembly 10 is intended foruse in an electronic calculator.

While keyboard switch assembly 10 incorporates a plurality of switchingsub-assemblies 28 each comprising one push button 22, one snap-actingdome switch member 14, and associated switch terminals and conductors onupper surface 26 of printed circuit board 12, each of the switchingsub-assemblies is similar and functionally identical and thusdescription of one such .[.subassembly.]. .Iadd.sub-assembly .Iaddend.28will suffice.

Referring now particularly to FIGS. 6 and 7, printed circuit board 12comprises a sheet of rigid plastic material having one surface 26 copperclad, the conductors and terminals on surface 26 being formed byphoto-engraving techniques as is well known to those skilled in the art.Each switching sub-assembly 28 comprises three switch terminals 30 onsurface 26 and disposed in an equilateral triangle, and a center switchterminal 32 on surface 26 disposed in the center of the triangle formedby outer terminals 30. In the particular switching sub-assembly 28-1shown in FIG. 6, two of the outer terminals 30-1 and 30-2 are connectedby conductor 34 on upper surface 26 of board 12, terminal 30-2 havinganother conductor 36 on upper surface 26 connected thereto. Due to thegeometry of the conductor pattern on the upper surface 26 of board 12,terminal 30-3 of switching sub-assembly 28-1 does not have a conductorconnected thereto however, in other of the switching sub-assemblies 28,all three of the switching terminals 30 may be connected by oneconductor. In the particular circuit board pattern shown outer terminal30-3' of switching sub-assembly 28-2 is also connected to conductor 34.

Central terminal 32 of switching assembly 28-1 is connected by conductor38 on upper surface 26 to external terminal 40. The other conductors onupper surface 26 of board 12, such as conductors 42, 44 and 46 whichpass through the triangle defined by outer terminals 30 of switchingassembly 28-1, connect other external terminals to the terminals ofother switching sub-assemblies.

Conductor 48 on upper surface 26 of board 12 partially surrounds centralterminal 32 of switching sub-assembly 28-1 being spaced therefrom andfrom conductor 38. In the particular printed circuit pattern shown,conductor 48 is connected in conductor 50 on upper surface 26 of board12 which connects external terminal 52 to a terminal of anotherswitching .[.subassembly.]. .Iadd.sub-assembly .Iaddend.28. In otherswitching sub-assemblies, such as .[.subassembly.]. .Iadd.sub-assembly.Iaddend.28-2, conductor 48' completely surrounds central terminal 32'and is connected to conductor 38' on upper surface 26 which connectscentral terminal 32' to external terminal 54.

Referring now particularly to FIG. 7, upper surface 26 of printedcircuit board 12 and the conductors thereon are covered with a thinlayer 56 of insulating material, terminals 30, 32 being masked duringapplication of insulative coating 56 so that the terminals are notso-coated. Terminals 30, 32 are preferably plated, such as by platingwith gold over nickel, as at 58.

While the conductors, terminals, insulative layer 56, and plating 58 areshown for purposes of illustration in FIGS. 5 and 7 as havingappreciable thickness, it will be understood that actually theseelements are very thin.

Referring now additionally to FIG. 8, in the preferred embodiment,snap-acting dome switch member 15 has a generally triangularconfiguration with apices 60 which are arcuately curved about center 62,apices defining flat sides 62 therebetween. Switch member 14 may also besaid to be generally circular with portions removed to form chords 62between arcuate portions 60. Projections or dimples 64 are formeddownwardly from apices 60 and a center projection or dimple 66 is formedprojecting into the interior of the dome.

Snap-acting dome switch member 14 of switching sub-assembly 28-1 isdisposed over and facing upper surface 26 of board 12, conductors 34-48,and center terminal 32, outer projections 64 respectively engaging outerterminals 30 and thus spacing the periphery of switch member 14 abovethe conductors and terminals, as best seen in FIG. 7. Center projection66 is in registry with and spaced from center terminal 32 in the normalposition of snap-acting dome switch member 14, as shown in solid linesin FIG. 7. Application of a downward force on switch member 14, as shownby an arrow 68, will deflect member 14 from its normal position to anon-overcenter position, as shown in dashed lines at 70, in which centerprojection 66 engages center contact 32 thereby electrically connectingcenter contact 32 to outer contacts 30 to complete the desiredelectrical circuit.

Conductor 48 partially surrounding center terminal 32 (or 48' completelysurrounding center terminal 32'), and its insulative coating 56, forms apad preventing damage to center projection 66 on snap-acting dome switchmember 14, i.e., application of excessive force in direction 68 onswitch member 14 will cause the area surrounding projection 66 to moveinto engagement with the insulation covering conductor 48 thuspreventing further downward movement of the dome and damage toprojection 66.

Retaining sheet 16, which covers insulative layer 56 on upper surface 26of circuit board 12, is formed of a sheet of relatively thin flexibleinsulating material and has openings 72 therein which respectivelyreceive and locate snap-acting dome switch members 14, openings 72generally conforming to the configuration of switch members 14 buthaving cut-out portions 74 respectively aligned with projections 64which respectively expose portions of outer terminals 30 (FIG. 9).

Cover sheet 18 is formed of an imperforate sheet of relatively thin,flexible insulating material and covers retaining sheet 16 and switchmembers 14. Cover member 20 covers sheet 18 and has openings 76 thereinwhich receive push buttons 22. Each push button 22 has an X-shapedprojection 78 formed on its bottom surface 80, projection 78 being inregistry with center projection 66 of the respective switch member 14.Projection 78 engages the area of cover sheet 18 over center projection66 but normally applies no force thereto other than what little force isattributable to its own weight which is insufficient to deflect switchmember 14 to its actuated position 70. Application of manual fingerpressure on a particular push button 22 results in the application offorce in direction 68 through cover sheet 18 on the respectivesnap-acting dome switch member 14 thereby actuating the switch member toits non-overcenter, deflected position 70 to perform the desiredswitching function. Upon release of manual finger pressure on pushbutton 22, the respective switch member 14 resiliently returns to itsnormal position thus opening the circuit previously established andreturning the respective push button 22 to its normal, inactiveposition.

Referring now to FIG. 11 in which like elements are indicated by likereference numerals and similar elements by primed reference numerals,here, each switching sub-assembly 28' comprises center terminal 32 onupper surface 26 of printed circuit board 12 and a single outer terminal30' also on upper surface 26, center terminal 32 and outer terminal 30'being connected by conductors (not shown) on upper surface 26 toexternal terminals (also not shown). Sheet 82 formed of relatively thininsulating material covers upper surface 26 and conductors 84 thereonand has openings 86, 88 respectively exposing terminals 30', 32.

In this embodiment, snap-acting dome switch member 14' has a generallyrectangular configuration with flat portion 90 integrally joined to theperiphery of domed portion 92. Projection 64' is formed from flatportion 90 and projection 66 is formed from the center area of dome 92.

Flat portion 90 of switch member 14' is supported on the upper surfaceof insulator 82 with projection 64' extending through opening 86 andengaging terminal 30', and with projection 66 in registry with opening88 and terminal 32. Insulative retaining member 16 covers insulator 82and has openings 72' therein which receive and locate switch members14', openings 72' conforming to the rectangular configuration of switchmembers 14'.

Cover sheet 18 covers retaining member 16 and cover member 20 (not shownin FIG. 11) in turn covers cover sheet 18 and has openings 76 thereinwhich receive and locate push buttons 22.

The switching action of the embodiment of FIGS. 11 and 12 is virtuallyidentical to that of FIGS. 4-10, i.e., application of manual fingerpressure on a push button 22 causes X-shaped projection 78 to applydownward force on the center area of a respective dome 92 through coversheet 18 thereby actuating dome 92 from its normal position, as shown inFIG. 11, to its non-overcenter, deflected position in which projection66 extends through opening 88 in insulator 82 and engages center contact32 thereby to provide the switching function.

Referring now to FIG. 13 in which like elements are indicated by likereference numbers and similar elements by primed reference numerals, amodification of the switch element of FIGS. 11 and 12 is shown having anadditional contact projection 65 formed in flat portion 90 on theopposite side of domed portion 92 from projection 64'.

Referring now to FIG. 14 in which like elements are again indicated bylike reference numerals and similar elements by double primed referencenumbers, a modification of the switching element 14 shown in FIGS. 4-10is shown (referring particularly to FIG. 8) in which domed switchingelement 14" has a generally rectangular configuration with arcuatecorners 60" joined by straight sides 62", contact projections or dimples64 being formed in corners 60". It will be observed that switchingelement 14" may be formed by cutting straight edges 62" from a circularsnap-acting dome.

While snap-acting dome switching elements have been shown in thepreferring embodiment, it will be understood that the audible andtactile feedback provided by the "oil canning" action of a dome is notrequired for the switching function and that other types of switchingelements can be employed; the basic requirement of the switching elementis that it be capable of being depressed to complete a circuit betweenrespective X and Y lines, have the required memory or resilience toreturn to its initial position upon removal of the actuating force, andhave a configuration which will make the required electrical connectionbetween a selected XY conductor pair when depressed without touchingother conductors interconnecting contact points for other switches onthe same board. While an insulating coating or layer is disclosedcovering the circuitry other than the terminal portions, such aninsulative coating or layer is not a requirement since with properarrangement of the conductive pattern and proper switch elementdeflection characteristics, the insulating coating can be eliminated.

The switching element configuration shown in FIGS. 8 and 14 is preferredsince the provision of three or four apices or corners will contactprojections or dimples therein provides resting points for the domearound the periphery thereof, the intermediate flat sides cut from thedome insuring proper alignment of the contact projections by the domeretaining sheet 16.

While the printed circuit board has been shown and described, it will bereadily understood that the XY conductors can be secured to one surfaceof an insulative board by means other than photo-engraving.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is: .[.1. In a keyboard switch assembly including a pushbutton manually actuable from an inactive to a switch-actuatingposition, and a conductive switch member including a resilient elementactuated by said push button from a normal to a deflected position andresiliently returning to its normal position upon removal of force fromsaid .[.bush.]. .Iadd.push .Iaddend.button, the improvement comprisingan insulative board having opposite surfaces, one only of said surfaceshaving first and second elongated conductors thereon, said firstconductor including a first switch terminal portion and said secondconductor including a second switch terminal portion, said conductorsand terminal portions being generally coplanar, said switch elementbeing positioned in facing relationship with said one surface and saidconductors, said switch element having first and second spaced contactareas thereon, said first contact area engaging said first terminalportion, said second contact area being in registry with said secondterminal portion and engaging the same when said element is in saiddeflected position thereby electrically connecting said first and secondterminal portions, and means for holding said push button, switch memberand board in operative relationship..]. The assembly of claim .[.1.]..Iadd.23 .Iaddend.further comprising a layer of insulating materialcovering said conductors excluding said terminal portions. .[.3. Theassembly of claim 2 wherein said element is a snap-acting dome, saidsecond contact area being at the center of said dome, said one surfaceof said board having a third conductor thereon at least partiallysurrounding said second terminal portion, closely spaced therefrom andgenerally coplanar therewith, the area of said dome surrounding saidsecond contact area engaging the insulation covering said thirdconductor upon further deflection of said dome following engagement ofsaid second contact area with said second terminal portion thereby toprotect said second contact area..].
 4. .[.The assembly of claim 1wherein.]. .Iadd.In a keyboard switch assembly including a push buttonmanually actuable from an inactive to a switch-actuating position, and aconductive switch member including a resilient element actuated by saidpush button from a normal to a deflected position and resilientlyreturning to its normal position upon removal of force from said pushbutton, the improvement comprising an insulative board having oppositesurfaces, one only of said surfaces having first and second elongatedconductors thereon, said first conductor including a first switchterminal portion and said second conductor including a second switchterminal portion, said conductors and terminal portions being generallycoplanar, said switch element being positioned in facing relationshipwith said one surface and said conductors, said switch element havingfirst and second spaced contact areas thereon, said first contact areaengaging said first terminal portion, said second contact area being inregistry with said second terminal portion and engaging the same whensaid element is in said deflected position thereby electricallyconnecting said first and second terminal portions, and means forholding said push button, switch member and board in operativerelationship, .Iaddend.said one surface of said board .[.has.]..Iadd.having .Iaddend.at least a third conductor thereon intermediateand spaced from said first and second conductors and generally coplanartherewith, said third conductor extending .Iadd.between said terminalportion and .Iaddend.under said element from a location on said onesurface remote therefrom, .Iadd.means for maintaining .Iaddend.saidelement in .[.its deflected position being spaced from.]. .Iadd.spacedrelationship with .Iaddend.said third conductor.[.,.]. .Iadd.in bothpositions of said element whereby .Iaddend.there .[.being.]. .Iadd.is.Iaddend.no electrical connection between said third conductor and saidelement in either position thereof.
 5. The assembly of claim 4 whereinsaid element is a snap-acting dome, said second contact area being atthe center of said dome.[., said third conductor being intermediate saidfirst and second terminal portions and generally coplanar therewith .]..6. .[.The assembly of claim 1 wherein.]. .Iadd.In a keyboard switchassembly including a push button manually actuable from an inactive to aswitch-actuating position, and a conductive switch member including aresilient element actuated by said push button from a normal to adeflected position and resiliently returning to its normal position uponremoval of force from said push button, the improvement comprising aninsulative board having opposite surfaces, one only of said surfaceshaving first and second elongated conductors thereon, said firstconductor including a first switch terminal portion and said secondconductor including a second switch terminal portion, said conductorsand terminal portions being generally coplanar, said switch elementbeing positioned in facing relationship with said one surface and saidconductors, said switch element having first and second spaced contactareas thereon, said first contact area engaging said first terminalportion, said second contact area being in registry with said secondterminal portion and engaging the same when said element is in saiddeflected position thereby electrically connecting said first and secondterminal portions, and means for holding said push button, switch memberand board in operative relationship, .Iaddend.said one surface of saidboard has a third conductor thereon at least partially surrounding saidsecond terminal portion, spaced therefrom and generally coplanartherewith, the area of said element surrounding said second contact areaengaging said third conductor upon further deflection of said elementfollowing engagement of said second contact with said second terminalportion thereby to protect said element and second contact area.
 7. Theassembly of claim .[.1.]. .Iadd.23 .Iaddend.wherein a section of atleast said second conductor extends under said .[.element.]..Iadd.device .Iaddend.from a location on said one surface remotetherefrom.
 8. The assembly of claim .[.1.]. .Iadd.23 .Iaddend.whereinsaid .[.element.]. .Iadd.device .Iaddend.is a snap-acting dome, saidsecond contact area being at the center of said dome.
 9. The assembly ofclaim 8 wherein said second contact area comprises a projection on theinterior of said dome.
 10. .[.The assembly of claim 8.]. .Iadd.In akeyboard switch assembly including a push button manually actuable froman inactive to a switch-actuating position, and a conductive switchmember including a resilient element actuated by said push button from anormal to a deflected position and resiliently returning to its normalposition upon removal of force from said push button, the improvementcomprising an insulative board having opposite surfaces, one only ofsaid surfaces having first and second elongated conductors thereon, saidfirst conductor including a first switch terminal portion and saidsecond conductor including a second switch terminal portion, saidconductors and terminal portions being generally coplanar, said switchelement being positioned in facing relationship with said one surfaceand said conductors, said switch element having first and second spacedcontact areas thereon, said first contact area engaging said firstterminal portion, said second contact area being in registry with saidsecond terminal portion and engaging the same when said element is insaid deflected position thereby electrically connecting said first andsecond terminal portions, and means for holding said push button, switchmember and board in operative relationship, wherein said element is asnap-acting dome, said second contact area being at the center of saiddome, .Iaddend.further comprising third, fourth and fifth switchterminals on said one surface of said board, said third through fifthterminals and said first terminal portion being arranged in a rectanglewith said second terminal portion in the interior thereof, said firstcontact area comprising a first projection formed from said domeadjacent the periphery thereof, said dome having second, third andfourth projections formed therefrom adjacent the periphery thereof andrespectively engaging said third, fourth and fifth switch terminals,said projections spacing the periphery of said dome from said onesurface of said board and said conductor, said second contact areacomprising a fifth projection formed from the interior of said dome. 11.The assembly of claim 10 wherein said switch element is generallyrectangular with arcuate corners coaxial with the center of said dome,said first through fourth projections being formed from said corners.12. .[.The assembly of claim 8 wherein.]. .Iadd.In a keyboard switchassembly including a push button manually actuable from an inactive to aswitch-actuating position, and a conductive switch member including aresilient element actuated by said push button from a normal to adeflected position and resiliently returning to its normal position uponremoval of force from said push button, the improvement comprising aninsulative board having opposite surfaces, one only of said surfaceshaving first and second elongated conductors thereon, said firstconductor including a first switch terminal portion and said secondconductor including a second switch terminal portion, said conductorsand terminal portions being generally coplanar, said switch elementbeing positioned in facing relationship with said one surface and saidconductors, said switch element having first and second spaced contactareas thereon, said first contact area engaging said first terminalportion, said second contact area being in registry with said secondterminal portion and engaging the same when said element is in saiddeflected position thereby electrically connecting said first and secondterminal portions, and means for holding said push button, switch memberand board in operative relationship, wherein said element is asnap-acting dome, said second contact area being at the center of saiddome, .Iaddend.said first contact area .[.comprises.]. .Iadd.comprising.Iaddend.a projection on said switch element spacing the periphery ofsaid dome from said one surface of said board and said conductors. 13.The assembly of claim 12 wherein said projection is formed from saiddome adjacent the periphery thereof.
 14. The assembly of claim 13wherein said switch member includes a flat portion joined to theperiphery of said dome, said projection being formed from said flatportion.
 15. .[.The assembly of claim 8.]. .Iadd.In a keyboard switchassembly including a push button manually actuable from an inactive to aswitch-actuating position, and a conductive switch member including aresilient element actuated by said push button from a normal to adeflected position and resiliently returning to its normal position uponremoval of force from said push button, the improvement comprising aninsulative board having opposite surfaces, one only of said surfaceshaving first and second elongated conductors thereon, said firstconductor including a first switch terminal portion and said secondconductor including a second switch terminal portion, said conductorsand terminal portions being generally coplanar, said switch elementbeing positioned in facing relationship with said one surface and saidconductors, said switch element having first and second spaced contactareas thereon, said first contact area engaging said first terminalportion, said second contact area being in registry with said secondterminal portion and engaging the same when said element is in saiddeflected position thereby electrically connecting said first and secondterminal portions, and means for holding said push button, switch memberand board in operative relationship, wherein said element is asnap-acting dome, said second contact area being at the center of saiddome and .Iaddend.further comprising third and fourth switch terminalson said one surface of said board, said third and fourth terminals andsaid first terminal portion being arranged in a triangle with saidsecond terminal portion in the interior thereof, said first contact areacomprising a first projection formed from said dome adjacent theperiphery thereof, said dome having second and third projections formedtherefrom adjacent the periphery thereof and respectively engaging saidthird and fourth switch terminals, said projections spacing theperiphery of said dome from said one surface of said board and saidconductors, said second contact area comprising a fourth projectionformed from the interior of said dome.
 16. The assembly of claim 15wherein said switch element is generally triangular with arcuate apicescoaxial with the center of said dome, said first, second and thirdprojections being formed from said apices.
 17. The assembly of claim 16wherein said holding means comprises a layer of insulating materialcovering said conductors excluding said terminal portions and terminals,a first sheet of insulating material covering said layer and having anopening therein receiving said switch element and conforming thereto forlocating the same, a second sheet of insulating material covering saidfirst sheet and switch element, and a plate member covering said secondsheet and having an opening therein receiving said push button, saidpush button acting on said dome through said second sheet. The assemblyof claim 16 wherein a section of at least said second conductor extendsunder said dome from a location on said one surface remote therefrom,said one surface of said board having a third conductor thereon at leastpartially surrounding said second terminal portion, spaced thereon andgenerally coplanar therewith, said conductors exclusive of said terminalportions having a layer of insulating material thereon, the area of saiddome surrounding said fourth projection engaging the insulation coveringsaid third conductor upon further deflection of said dome followingengagement of said second contact area with said second terminal portionthereby to protect said fourth projection.
 19. The assembly of claim 18wherein said third conductor completely surrounds said second terminalportion and is joined to said second conductor.
 20. The assembly ofclaim 18 wherein said third conductor partially surrounds said secondterminal portion and is joined to a fourth conductor on said one surfaceof said board which extends under said dome.
 21. The assembly of claim18 wherein said first conductor is joined to at least said .[.second.]..Iadd.third .Iaddend.terminal.
 22. The assembly of claim 18 wherein saidboard has a fourth conductor thereon which extends under said dome..Iadd.
 23. In a keyboard switch assembly including a resilient,conductive switch device manually actuable from a normal to a deflectedposition, said switch device resiliently returning to its normalposition upon removal of force therefrom, the improvement comprising aninsulative member having opposite surfaces, one of said surfaces havingfirst and second elongated conductors thereon, said first conductorincluding a first switch terminal portion and said second conductorincluding a second switch terminal portion, said conductors and terminalportions being generally coplanar, said switch device being positionedin facing relationship with said one surface and said conductors, saidswitch device having first and second spaced contact areas thereon, saidcontact areas being respectively in registry with said terminal portionsand engaging the same when said device is in said deflected positionthereby electrically connecting said terminal portions, at least one ofsaid contact areas being spaced from the respective terminal portion insaid normal position of said device, said one surface of said memberhaving at least a third conductor thereon intermediate and spaced fromsaid first and second conductors and generally coplanar therewith, saidthird conductor extending between said contact areas and under saiddevice from a location on said one surface remote therefrom, means formaintaining said device in spaced relationship with said third conductorin both positions of said device whereby there is no electricalconnection between said third conductor and said device in eitherposition thereof, and means for holding said switch device andinsulative member in operative relationship. .Iaddend..Iadd.
 24. Theassembly of claim 8 further comprising third and fourth switch terminalson said one surface of said member, said third and fourth terminals andsaid first terminal portion being arranged in a triangle with saidsecond terminal portion in the interior thereof, said first contact areacomprising a first projection formed from said dome adjacent theperiphery thereof, said dome having second and third projections formedtherefrom adjacent the periphery thereof and respectively engaging saidthird and fourth switch terminals, said projections spacing theperiphery of said dome from said one surface of said board and saidconductors, said second contact area comprising a fourth projectionformed from the interior of said dome, said maintaining means comprisingsaid first, second and third projections. .Iaddend..Iadd.
 25. Theassembly of claim 24 wherein said switch device is generally triangularwith arcuate apices coaxial with the center of said dome, said first,second and third projections being formed from said apices. .Iaddend..Iadd.
 26. The assembly of claim 2 wherein said device is a snap-actingdome, said first contact area engaging said first terminal portion inboth positions of said device, said second contact area being at thecenter of said dome and being spaced from said second contact area insaid normal position of said device, said one surface of said memberhaving a fourth conductor thereon spaced from said third conductor andfirst terminal portion and at least partially surrounding said secondterminal portion, closely spaced therefrom and generally coplanartherewith, the area of said dome surrounding said second contact areaengaging the insulation covering said fourth conductor upon furtherdeflection of said dome following engagement of said second contact areawith said second terminal portion thereby to protect said second contactarea. .Iaddend.